1. Field of the Invention
This invention relates in general to methods and systems involving cameras and, more particularly, to providing navigational aid and difference extraction.
2. Description of the Related Art
To observe changes of an object or scene, repeat photos are sometimes taken. The most famous examples in the field of “repeat photography” or “rephotography” are applications to historic buildings or nature that show changes over time. For example, rephotographers take pictures of mountains or buildings from the same camera angle and position as photos that had been taken years ago, as can be seen in the USGS Repeat Photography Project and VERTIGO. In the manufacturing area, repeat photography for examination is also practiced. For example, in order to compare two industrial parts where one part has a problem and another part works well, pictures are taken of both parts to compare the difference. However, it is not easy to take pictures of an object twice from the same camera angle when using a handheld camera.
To take photos from the same camera angle, geometrical relationships between the object and the camera have to be estimated. There are many methods to estimate a camera pose, and to match photos of an object with its 3D model. The Viewfinder and Marmota projects match scene photos to corresponding 3D models in Google Earth (“Environmental Content Creation and Visualisation in the ‘Future Internet’”, John Domingue and Dieter Fensel and Paolo Traverso, FIS2008, 2008). Camera poses can also be estimated from an object using its 3D CAD model (“Tracking of Industrial Objects by using CAD models” Harald Wuest and Didier Stricker, Journal of Virtual Reality and Broadcasting, Vol. 4, No. 1, 2007).
There is a need for systems and methods that can guide the user in real time to the same camera position and angle from which a previous shot was taken.